In the past, in the case of measuring concentrations of various types of components in exhaust gas, or various types of components generated or processed in various types of processes, various types of gas analyzers have been used, such as a non-dispersive infrared gas analyzer (NDIR), non-dispersive ultraviolet gas analyzer (NDUV), magnetic oxygen analyzer, chemiluminescence detecting type nitrogen oxide analyzer (CLD type NOx analyzer), and hydrogen flame ionization detector (FID) (Patent literature 1). In a gas analyzing system provided with such a gas analyzer, before measurement, calibration using zero gas and span gas is performed. In such calibration, first, the zero gas is flowed through the gas analyzer to perform zero calibration, and then the span gas is flowed through the gas analyzer to perform span calibration.
Such zero gas or span gas is generally filled in a high-pressure cylinder, and supplied to the gas analyzing system through a supply line for each gas; however, if calibration has not been performed for a long time, concentration of the span gas remaining in various types of pipes constituting a span gas supply line may be varied, or the gas itself may be denatured or deteriorated.
More specifically, in the case where the span gas supply line is formed of resin pipes such as fluorine resin pipes or nylon pipes, the span gas, or gas in outside air, such as CO2 or O2 may permeate the resin pipes to thereby vary the gas concentration. Also, in the case where the span gas supply line is formed of pipes made of metal, such as stainless steel pipes, some component (e.g., nickel in the case of the stainless steel pipes) contained in the meal may act as a catalyst to denature the span gas.
Even if the calibration is performed with use of the span gas deteriorated as described, appropriate calibration is not performed to cause reductions in accuracy and reliability of an analysis result.